Spray resulting from misdirected drops is frequently observed for thermal ink-jet heads. The problem is considerably worse for printing in the "multidrop" mode, that is, printing groups of drops in bursts at 50 kHz drop rates.
Experiments have shown that alignment between the resistor and orifice in the thermal head is a critical factor influencing the direction of exiting drops. For heads employing the three-sided barrier structure, perfect alignment of the orifice over the resistor has been found not to be the ideal condition.
U.S. Pat. No. 4,330,787 describes a thermal ink-jet printer in which the angle between the normals to the plane of the resistor and the plane of the orifice are between 0.degree. and 90.degree.. However, changing the angle between the resistor and orifice still does not provide the printing quality required.